Brochosomal-based defence against infection by the entomopathogenic fungus, Beauveria bassiana in the tea green leafhopper (Empoasca onukii)

• Brochosomes were casued shrivelling and dehydration of fungal conidia and inhibition of the growth of germinated hyphae. • Brochosomes on the surface of leafhoppers are detachable, which enables leafhoppers to remove most spores adhered to their body surface through self-cleaning behavior. • At joint regions, wing edges, and other areas with sparse brochosome coverage, Beauveria bassiana conidia can successfully adhere and establish infection. • Brochosomes were not degraded by fungal secretions, and with the help of surfactant, brochosomes were deformed and absorbed by hyphae. Beauveria bassiana is an important fungal biological control agent against many insect pests including the tea green leafhopper ( Empoasca onukii ), but its field efficacy is often poor due to low infection efficiency. The body surface of E. onukii is covered with a layer of hollow honeycomb-like micro-nanospherical particles termed brochosomes. These are known to confer superhydrophobicity to the insect’s integument, and very recent work with the corn leafhopper, Dalbulus maidis, has shown they, in combination with self-cleaning but the insect, can reduce infection by entomopathogenic fungi. Here we used fungal spray inoculation studies, fluorescence labeling, and scanning electron microscopy (SEM) to explore the role of brochosomes on B. bassiana infection of E. onukii . Brochosomes were casued shrivelling and dehydration of fungal conidia and inhibition of the growth of germinated hyphae. After 56 h of incubation after treatment with fungal conidia, newly secreted brochosomes had encapsulated conidia thought on wing surfaces but not on the head, thorax, and legs with less dense brochosomes. A large number of structurally intact brochosomes were adsorbed onto the surface of hyphae, and these brochosomes were not degraded by fungal secretions. When surfactant was combined with conidial suspension, brochosomes were deformed and absorbed by hyphae, indicating that the structural integrity of brochosomes is key to their protective function. Additionally, manual removal of brochosomes from the wings of E. onukii allowed normal appressoria development from conidia and establishment of colonies within 48 h. Fluorescence labeling revealed that self cleaning by E. onukii removed most conidia. This study confirms that brochosomes, complement self cleaning to protect E. onukii from B. bassiana infection. Accordingly, adjuvants need to be added to B. bassiana applications to maximise field control of this major tea pests.